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Date: Mon, 11 Jul 2011 20:22:54 +0400
From: Solar Designer <>
To: Ludwig Nussel <>
Cc:, Michael Matz <>,
	Thorsten Kukuk <>, Andreas Jaeger <>,
	Zefram <>
Subject: Re: CVE request: crypt_blowfish 8-bit character mishandling

On Mon, Jul 11, 2011 at 04:39:08PM +0200, Ludwig Nussel wrote:
> Solar Designer wrote:
> >[...]
> >Also, it brings up the question: why merely use $2a$ running the new
> >code rather than fully emulate the bug even for newly set passwords,
> >which would make all passwords work, even on other networked machines?
> >Sure, that would be even nastier for security, so maybe you managed to
> >strike a balance well.  But nevertheless the question is there.  One of
> >your options results in full backwards compatibility at a security cost
> >(for the local system), but the other somehow chooses to strike a
> >balance between compatibility and security without achieving either of
> >these fully (for a network of systems).
> >
> >Maybe you can afford to drop BLOWFISH_2y to avoid those inconsistencies?
> >I imagine that people won't know to enable this option unless/until they
> >have already run into an issue anyway (that is, someone is already
> >unable to log in).  At this point, they could likely upgrade the rest of
> >their networked systems as well... or downgrade this one. ;-(
> I'm not sure I understand what you are suggesting.

I am not exactly suggesting anything specific as I don't know your
priorities, but I point out the inconsistency.

My preference would be that you don't implement that BLOWFISH_2y option -
always have new hashes generated as 2y, even though this means that
networked systems need to be upgraded to new package versions in sync.

> Keep using the buggy
> algorithm for new passwords and keep storing them as 2a

I'd be unhappy about that, but it's a valid option to provide if you
want to minimize user annoyance, including for networked systems that
are not upgraded in sync (but are manually configured for this...)

> as long as BLOWFISH_2a2x is turned on?

No, you'd need a separate option (or a tri-state option) such that
there's a way for non-networked systems to gradually migrate to 2y
hashes without annoying any users.


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